Friction stir welding is a joining method. In the friction stir welding, a pin is rotated at a high speed to generate frictional heat and cause plastic flow in materials to be joined to thereby form a homogenized weld joint. For this welding process, a tool comprised of a probe having a pin part, and a holder for holding the probe is used. The probe is consumable and has relatively high exchange frequency. The holder is therefore required to allow easy replacement of the probe.
A friction stir welding tool having a probe removably attached to a holder is known as disclosed in Patent Document 1, for example. FIG. 8 hereof shows in cross section the friction stir welding tool disclosed in Patent Document 1.
Referring now to FIG. 8, the tool 100 is constituted by a holder 102 having an axial hole 101, a probe 103 inserted in the axial hole 101 from below, and a set bolt 104 screwed into the holder 102 for setting the probe 103 with the probe 103 urged by a front end face of the set bolt 104.
When friction stir welding is to be achieved, the holder 102 is rotated at a high speed to thereby rotate the probe 103 at the same high speed. During welding, the probe 103 is subjected to external force such as minute vibration, which may cause loosening of the set bolt 104. To avoid this problem from occurring, frequent retightening of the set bolt 104 is required. This will lower the working efficiency, leading to deterioration of the productivity. Furthermore, when the probe 103 is subjected to an overload during welding process, excessive tightening of the set screw 104 may occur. The over-tightening makes it difficult to remove the set screw when the probe is to be replaced.
Concurrently with a demand for increased productively, there is a need for a friction stir welding tool which is capable of preventing loosening and over-tightening of a set bolt.